The field of this invention is labyrinth seal design as well as a particular application to a lock for a hydrostatically set packer.
Hydrostatically set devices for subterranean wells such as packers in the past have relied on an initially locked piston. When the packer was placed at the desired depth, the locking mechanism was released, generally by pressurization of the wellbore, or an electromechanical device or system. The electromechanical devices include, but are not limited to, systems that rely on acoustic, pressure pulse, or vibratory communication methods to enable the setting sequence of the packer or other downhole device. The applied wellbore pressure would break a rupture disc to expose the lock to hydrostatic pressure. In the embodiment of the electromechanical device, the device would expose the lock to hydrostatic pressure. Hydrostatic pressure, acting on one side of the lock against an atmospheric chamber on the other side of the lock, allowed the lock to move. Release of the lock permits piston movement. The piston moves due to the force of hydrostatic pressure across the piston which would set the slips and compress the seal against the borehole wall or tubular, or otherwise actuate the device. A lock ring would hold the set.
A potential problem with this known design was that seal leakage could allow pressure to prematurely communicate to one side of the lock so that the packer would be prematurely unlocked and consequently, hydrostatically set. Thus, an objective of the present invention is to acknowledge that seal leakage is a potential occurrence with drastic and expensive consequences and to deal with that possibility. The objective is met using a wide variety of labyrinth seals on the lock sleeve assembly. Even if leakage of the seals below a predetermined level were to occur, the labyrinth seal would prevent a net force from occurring on the lock sleeve, thus preventing premature hydrostatic setting of the packer.
Labyrinth seals have been used in different tools in downhole applications. They have been used in perforating guns, as shown in U.S. Pat. Nos. 4,886,126 and 5,680,905. They have been used in downhole turbo-machines, U.S. Pat. No. 4,264,285 and in a fluid flow regulator, U.S. Pat. No. 4,858,644. Hydraulically released locks for packers have been used in U.S. Pat. No. 5,320,183.
U.S. Pat. No. 5,720,349 shows the use of a labyrinth seal in an assembly of an anchor, whipstock, and a starter mill. The labyrinth seal compensates for thermal expansion of a fluid filled system to prevent setting of the anchor due to pressure that would have otherwise built up due to thermal effects. This device is focused on compensation for pressure from thermal expansion. On the other hand, U.S. Pat. No. 5,689,905, in the context of a perforating gun, is focused on use of the labyrinth seal to prevent premature actuation of the gun due to seal leakage. Those skilled in the art will appreciate the scope of this invention from the description of the preferred embodiment, which appears below and the claims, which appear thereafter.
A hydrostatically set packer is disclosed. The actuating piston is locked for run in by a lock sleeve and lock dog arrangement. When the desired depth is reached well pressure is built up to break a rupture disc to allow hydrostatic pressure to act on one side of a lock sleeve. The other side of the lock sleeve is exposed to a chamber under atmospheric or low pressure. Movement of the lock sleeve releases the lock dog allowing piston movement to set the packer. The lock sleeve has a labyrinth seal so that seal leakage below a predetermined level will not prematurely activate the piston lock and prematurely set the packer. A variety of designs for the labyrinth are described.